<template>
  <div id="hy-swiper">
    <div class="swiper" @touchstart="touchStart" @touchmove="touchMove" @touchend="touchEnd">
      <slot></slot>
    </div>
    <slot name="indicator"> </slot>
    <div class="indicator">
      <slot name="indicator" v-if="showIndicator && slideCount > 1">
        <div v-for="(item, index) in slideCount" class="indi-item" :class="{ active: index === currentIndex - 1 }" :key="index"></div>
      </slot>
    </div>
  </div>
</template>

<script>
  export default {
    name: 'Swiper',
    props: {
      //多久一张图片
      interval: {
        type: Number,
        default: 3000
      },
      //延迟多久开始轮播
      animDuration: {
        type: Number,
        default: 300
      },
      //拖动多少比例弹回或移动下一张
      moveRatio: {
        type: Number,
        default: 0.25
      },
      //指示器 轮播图下面的小点 默认显示
      showIndicator: {
        type: Boolean,
        default: true
      }
    },
    data: function () {
      return {
        slideCount: 0, // 元素个数
        totalWidth: 0, // swiper的宽度
        swiperStyle: {}, // swiper样式
        currentIndex: 1, // 当前的index
        scrolling: false // 是否正在滚动
      }
    },
    mounted: function () {
      // 1.操作DOM, 在前后添加Slide
      setTimeout(() => {
        this.handleDom()

        // 2.开启定时器
        this.startTimer()
      }, 100)
    },
    methods: {
      /**
       * 定时器操作
       */
      startTimer: function () {
        this.playTimer = window.setInterval(() => {
          this.currentIndex++
          this.scrollContent(-this.currentIndex * this.totalWidth)
        }, this.interval)
      },
      stopTimer: function () {
        window.clearInterval(this.playTimer)
      },

      /**
       * 滚动到正确的位置
       */
      scrollContent: function (currentPosition) {
        // 0.设置正在滚动
        this.scrolling = true

        // 1.开始滚动动画
        this.swiperStyle.transition = 'transform ' + this.animDuration + 'ms'
        this.setTransform(currentPosition)

        // 2.判断滚动到的位置
        this.checkPosition()

        // 4.滚动完成
        this.scrolling = false
      },

      /**
       * 校验正确的位置
       */
      checkPosition: function () {
        window.setTimeout(() => {
          // 1.校验正确的位置
          this.swiperStyle.transition = '0ms'
          if (this.currentIndex >= this.slideCount + 1) {
            this.currentIndex = 1
            this.setTransform(-this.currentIndex * this.totalWidth)
          } else if (this.currentIndex <= 0) {
            this.currentIndex = this.slideCount
            this.setTransform(-this.currentIndex * this.totalWidth)
          }

          // 2.结束移动后的回调
          this.$emit('transitionEnd', this.currentIndex - 1)
        }, this.animDuration)
      },

      /**
       * 设置滚动的位置
       */
      setTransform: function (position) {
        this.swiperStyle.transform = `translate3d(${position}px, 0, 0)`
        this.swiperStyle['-webkit-transform'] = `translate3d(${position}px), 0, 0`
        this.swiperStyle['-ms-transform'] = `translate3d(${position}px), 0, 0`
      },

      /**
       * 操作DOM, 在DOM前后添加Slide
       */
      handleDom: function () {
        // 1.获取要操作的元素
        let swiperEl = document.querySelector('.swiper')
        let slidesEls = swiperEl.getElementsByClassName('slide')

        // 2.保存个数
        this.slideCount = slidesEls.length

        // 3.如果大于1个, 那么在前后分别添加一个slide
        if (this.slideCount > 1) {
          let cloneFirst = slidesEls[0].cloneNode(true)
          let cloneLast = slidesEls[this.slideCount - 1].cloneNode(true)
          swiperEl.insertBefore(cloneLast, slidesEls[0])
          swiperEl.appendChild(cloneFirst)
          this.totalWidth = swiperEl.offsetWidth
          this.swiperStyle = swiperEl.style
        }

        // 4.让swiper元素, 显示第一个(目前是显示前面添加的最后一个元素)
        this.setTransform(-this.totalWidth)
      },

      /**
       * 拖动事件的处理
       */
      touchStart: function (e) {
        // 1.如果正在滚动, 不可以拖动
        if (this.scrolling) return

        // 2.停止定时器
        this.stopTimer()

        // 3.保存开始滚动的位置
        this.startX = e.touches[0].pageX
      },

      touchMove: function (e) {
        // 1.计算出用户拖动的距离
        this.currentX = e.touches[0].pageX
        this.distance = this.currentX - this.startX
        let currentPosition = -this.currentIndex * this.totalWidth
        let moveDistance = this.distance + currentPosition

        // 2.设置当前的位置
        this.setTransform(moveDistance)
      },

      touchEnd: function (e) {
        // 1.获取移动的距离
        let currentMove = Math.abs(this.distance)

        // 2.判断最终的距离
        if (this.distance === 0) {
          return
        } else if (this.distance > 0 && currentMove > this.totalWidth * this.moveRatio) {
          // 右边移动超过0.5
          this.currentIndex--
        } else if (this.distance < 0 && currentMove > this.totalWidth * this.moveRatio) {
          // 向左移动超过0.5
          this.currentIndex++
        }

        // 3.移动到正确的位置
        this.scrollContent(-this.currentIndex * this.totalWidth)

        // 4.移动完成后重新开启定时器
        this.startTimer()
      },

      /**
       * 控制上一个, 下一个
       */
      previous: function () {
        this.changeItem(-1)
      },

      next: function () {
        this.changeItem(1)
      },

      changeItem: function (num) {
        // 1.移除定时器
        this.stopTimer()

        // 2.修改index和位置
        this.currentIndex += num
        this.scrollContent(-this.currentIndex * this.totalWidth)

        // 3.添加定时器
        this.startTimer()
      }
    }
  }
</script>

<style scoped>
#hy-swiper {
  overflow: hidden;
  position: relative;
}

.swiper {
  display: flex;
}

.indicator {
  display: flex;
  justify-content: center;
  position: absolute;
  width: 100%;
  bottom: 8px;
}

.indi-item {
  box-sizing: border-box;
  width: 8px;
  height: 8px;
  border-radius: 4px;
  background-color: #fff;
  line-height: 8px;
  text-align: center;
  font-size: 12px;
  margin: 0 5px;
}

.indi-item.active {
  background-color: rgba(212, 62, 46, 1);
}
</style>
